The present invention is directed to the synthesis of organopolysiloxanes having alkynyl radicals attached to silicon by carbon-silicon linkages and to their use. More particularly, the present invention relates to heat curable organopolysiloxane compositions utilizing alkynyl substituted organopolysiloxanes in combination with a hydride siloxane crosslinker and a Group 8-10 metal catalyst, such as a platinum catalyst.
Prior to the present invention, as shown by European patent application 0352493, one part heat curable thermosetting organosiloxane compositions were provided using an organopolysiloxane, a micro encapsulated hydrosilylation catalyst, an organohydrogenpolysiloxane and inhibitor in the form of compounds having at least one alkynyl group, such as an acetylenic alcohol. One part heat curable organopolysiloxanes are also shown by Weitemeyer et al, U.S. Pat. No. 4,906,721 having an organopolysiloxane with acetylenic groups attached to silicon by carbon-oxygen-silicon linkages, organopolysiloxanes with SiH groups and a platinum catalyst in the form of a platinum complex. The organopolysiloxanes compositions provided by Weitemeyer et al also have a room temperature stability of about 7 days and cure rapidly at elevated temperatures. Even though the cure of the Weitemeyer et al organopolysiloxane compositions having alkynyloxy groups joined to silicon by carbon-oxygen-silicon linkages is inhibited, these organopolysiloxanes are inherently hydrolytically unstable. As a result, the shelf stability of one part heat curable mixtures containing such hydrolytically unstable organopolysiloxane can be adversely affected. Improvement in the shelf stability of such one part heat curable organopolysiloxane compositions can be achieved, if the alkynyl substituted organopolysiloxanes are freshly prepared prior to mixing with the platinum catalyst and crosslinker.